Copper is increasingly replacing aluminum in interconnects fabrication in ultra-large-scale (ULSI) microelectronic devices. Nevertheless, this technology faces a few problems such as metal corrosion, weak adhesion, high chemical reactivity, and considerable diffusion of copper in silicon. One of the recent approaches to successfully address these issues is the formation of barrier/capping layer by electroless deposition. Thin films of Co(W,P) and Ni(Re,P) prepared by electroless deposition have already been shown to have potential application as barrier/capping layers on copper interconnects. These films provide significantly lower resistivity than other barriers and the formation of very thin, selective, and conformal deposition can be achieved through the electroless deposition.
Several related deposition chemistries shown in Table 1 have been developed and published recently for depositing phosphorous-containing cobalt or nickel-based amorphous barriers.
TABLE 1Componentsand operatingConcentration of components (g/l)conditionsPat. 3***Pat. 2**Pat. 1*43κ, 54κ21κ, 32κ1λ8π9θCobalt sulfate23232310-30heptahydrateCobalt3043030-6030-6030-60chloride hexahydrateSodium hypophosphite20152021212110-20Ammonium25-50hypophosphite(TMA)H2PO210-2010-20Sodium1012 0-30  0-3010-30tungstateAmmonium1010-3010-30tungstateTungsten13.5-70  phosphoricacid(TMA)2WO410-30Boric acid3131Sodium citrate84.5308013013020-80Ammonium 25-100citrate(TMA)3C6H4O720-8020-80dihydrateAmmonium50chlorideAmmoniumsulfateSodium borate4decahydrateRhodafac 6100.050.050.050.050.050.50.50.5pH9.58.3-8.77.5-9.098.9-9.0?????? 8-10pH adjustmentNaOH/KOH??????TMAHTemperature/° C.9578-8775-9085-9590-95??????60-801* U.S. Pat. No. 5,695,810 December 1997 Dubin et al. 2** U.S. Pat. No. 4,231,813 November 1980 Carlin 3*** U.S. Pat. No. 6,165,902 December 2000 Pramanick et al. λYosi Shacham-Diamand, Y. Sverdlov, N. Petrov: “Electroless Deposition of Thin-Film Cobalt-Tungsten-Phosphorus Layers Using Tungsten Phosphoric Acid (H3[P(W3O10)4]) for ULSI and MEMS Applications” Journal of The Electrochemical Society 148 (3), C162-C167 (2001). 1κA. Kohn, M. Eizenberg, Y. Shacham-Diamand, Y. Sverdlov: “Characterization of electroless deposited Co (W, P) thin films for encapsulation of copper metallization” Materials Science and Engineering A302, 18-25 (2001). 2κA. Kohn, M. Eizenberg, Y. Shacham-Diamand, B. Israel, Y. Sverdlov: “Evaluation of electroless deposited Co (W, P) thin films as diffusion barriers for copper metallization” Microelectronic Engineering 55, 297-303 (2001). 3κY. Shacham-Diamand, Y. Sverdlov: “Electrochemically deposited thin film alloys for ULSI and MEMS applications” Microelectronic Engineering 50, 525-531 (2000). 4κYosi Shacham-Diamand, Barak Israel, Yelena Sverdlov: “The electrical and material properties of MOS capacitors with electrolessly deposited integrated copper gate” Microelectronic Engineering 55, 313-322 (2001). πYosi Shacham-Diamand, Sergey Lopatin: “Integrated electroless metallization for ULSI” Electrochimica Acta 44, 3639-3649 (1999). θY. Segawa, H. Horikoshi, H. Ohtorii, K. Tai, N. Komai, S. Sato, S. Takahashi, Y. Ohoka, Z. Yasuda, M. Ishihara, A. Yoshio, T. Nogami: “Manufacturing-ready Selectivity of CoWP Capping on Damascene Copper Interconnects” (2001) 
A common disadvantage of all known compositions and processes mentioned in Table 1 is that films deposited from the solutions of the aforementioned compounds contains alkali-metal i.e., of Na and K in various alkali metals in concentrations significantly exceeding 2×10−4 atomic % (2 ppm). It is well known, however, that high concentrations of Na and K, which have high mobility, is unacceptable for functional layers of semiconductor wafers used in the manufacture of semiconductor devices. More specifically, the detrimental effect of alkali metals is primarily related to their easy penetration into silicon dioxide and microelectronic components.
Other drawbacks of some of the known solution compositions and processes listed in Table 1 are the following: an increased amount of highly-volatile, contaminating, and toxic components in an electroless deposition solution; relatively noticeable toxicity of some compositions; insufficient anti-corrosive properties of the deposited films; increased amount of ions of precipitation metals with a high degree of oxidation; and non-optimal concentrations of complexing agents required for obtaining deposited films with desired properties.